March 29, 2013

A handheld reader (top right) wirelessly powers and interrogates a tiny blood-pressure sensor embedded inside a prosthetic graft, inserted in this case as a conduit for hemodialysis in a patient with kidney failure (credit: A*STAR Institute of Microelectronics)

Researchers at A*STAR Institute of Microelectronics in Singapore are developing a prototype wireless device that powers an implanted blood-pressure sensor, eliminating the need to recharge or replace a battery.

The implant is powered by a handheld external reader, which uses inductive coupling to wirelessly transfer energy. The team developed an ultralow-power application-specific integrated circuit (ASIC) for the implant designed for low-power (21.6 μW) use.

The sensors are based on piezoresistive silicon nanowires. As blood flows over the sensor, the associated mechanical stresses induce a measurable increase in electrical resistance, proportional to the flow pressure.

“Our flow sensor system achieves an ultra-low power consumption of 12.6 microwatts,” said A*STAR’s Jia Hao Cheong, who heads the project. To achieve that the sensor transmits its data to the handheld reader passively, by backscattering some of the incoming energy. “We have tested our system with 50-millimeter-thick tissue between the external coil and implantable coil, and it successfully extracted the pressure data from the implantable device.”

“The next step of the project is to integrate the system and embed it inside a graft for an experimental animal,” Cheong said.